The present invention relates to a water-trapping agent disposed inside a hermetically sealed container to capture or trap moisture generated in an electronic part for a long period of time, and an organoelectronic device in which the water-trapping agent is disposed.
In recent years, organic EL (electroluminescence) elements, organic light emitting system such as organic EL display and organic EL illumination, and organic electronic device such as organic semiconductor and organic solar battery have been widely studied and investigated, and are expected to be applied to a wide variety of basic elements and other use.
The organic EL element comprises an organic EL layer of a thin film containing a luminescent organic compound sandwiched between a pair of electrodes, a cathode and an anode. The organic EL element is a spontaneous light-emitting element in which a hole and an electron are injected into the thin film and recombined to generate an exiton and which utilizes emission of light (fluorescence/phosphorescence) when the exiton is inactivated.
The most significant problem of the above-described organic EL element is to improve its durability and, above all, generation of non-light emitting portion called “dark spot” and the prevention of its growth. When the diameter of the dark spot grows in tens of micrometers (μm), the non-light emitting portion can be confirmed by visual observation. A principal cause of the dark spot generation is the influence of water and oxygen, and particularly water, which has been known to influence the element most seriously even in a trace amount.
It is, therefore, necessary to prevent water from penetrating into the organic EL element, which is presently represented by a hollow sealing structure as disclosed in JP 2002-33187A. In accordance with the hollow sealing structure, the penetration of moisture or oxygen into the organic EL element can be controlled or prevented by sealing the organic EL element under dry inert gas atmosphere.
With reference to FIG. 8, the anode 35 of ITO film is formed on an element substrate 32 having insulating and translucent properties in the hollow sealing structure of organic EL element 31. An organic EL layer 34 is formed as a thin layer on the upper surface of the anode 35 by a PVD method such as molecular beam deposition method, resistive heating method, and the like. The organic EL layer 34 comprises three layers of a copper phthalocyanine (CuPc) layer 4a as a hole injection layer formed on the upper surface of the anode 35, a Bis((N-(1-naphtyl-n-phenyl))benzidine (α-NPD) layer 34b as a hole transport layer formed on the upper surface of the layer 4a, and a tris(8-quinolinolat)aluminum (Alq3) layer 34c as a light-emitting and electron transport layer formed on the upper surface of the layer 34b. The light-emitting part is formed by a laminate comprising the aforementioned anode 35, the organic EL layer 34, and a cathode 36 described later. The cathode 36 is formed as a metal thin film formed on the upper surface of the light-emitting and electron transport layer 34c. A part of the cathode 36 is pulled out to the end of the element substrate 32 and connected to a driving circuit (not shown). The drying film 37 is placed as a drying means on the substrate 32 and/or sealing cap 33 in the container which is hermetically sealed by the substrate 32, sealing cap 33 and adhesive 38.
However, in the above hollow sealing structure, due to insufficient sealing properties of drying means such as inorganic drying sheet should be disposed inside the container so as to chemically or physically adsorb moisture therein. In this case, the space for disposing the drying means should be made in the container, which accordingly increases the cost for manufacture. Moreover, nothing is in contact with the upper surface of the cathode, and heat can only be emitted via radiation and convection across a panel. For the reason as set forth above, heat cannot be sufficiently radiated away from, for example, organic EL for illumination. Further, due to the use of larger panel, deflection can be created in the center portion of the panel, thereby causing the panel to break when being in contact with other element(s) disposed therein.
In order to overcome the above drawbacks and problems, there has been suggested that the speed of moisture or oxygen penetration can be decreased by sealing the organic layer by means of the membrane of resin and/or glass. For more detail, see JP 2002-33187(A). In this constitution, heat emission and panel strength properties can be improved over the conventional technologies.
With reference to FIG. 9, the anode 45 of ITO film is formed on the upper surface of an element substrate 42 having insulating and translucent properties. An organic layer 44 is formed as a thin film on the upper surface of the anode 45 by a PVD method such as molecular beam deposition method, resistive heating method, and the like. The organic layer 44 comprises four layers of a copper phthalocyanine (CuPc) layer 44a as a hole injection layer formed on the upper surface of the anode 45, a Bis((N-(1-naphtyl-n-phenyl))benzidine (α-NPD) layer 44b as a hole transport layer formed on the upper surface of the hole injection layer 44a, a tris(8-quinolinolat)aluminum (Alq3) layer 44c as a light-emitting layer formed on the upper surface of the hole transport layer 44b, and a LiF layer 44d as an electron injection layer formed on the upper surface of the light-emitting layer 44c. A cathode 46 is formed as a metal thin film formed on the upper surface of the light-emitting layer 44d of the organic layer 44, and is protected from moisture penetration via a buffer layer 47 by a passivation layer 48 which is made of SiN, SiON, or SiO2, and is formed thereon by physical vapor deposition method. A container is hermetically sealed by the element substrate 42, a sealing cap 43 and adhesive 49.
However, in a top emission-type solid sealing structure in which EL light generated from organic EL element is outwardly emitted from a sealing cap, it is hard to dispose drying agent, which does not have translucent properties, on a protective substrate from which light is emitted. In a case where drying agent is not employed, in order to guarantee sealing properties a passivation layer involving complicated process should be formed as a protective layer for the organic layer, thereby causing manufacturing cost and time to increase.
In view of the above, organic EL element disposed on the substrate may be sealed by a sealing cap, and water-trapping agent may be supplied into the inside of the above structure which is sealed by the substrate and the sealing cap so as to suppress or prevent dark spot generation. However, organic solvent is added to conventional translucent water-trapping agent so as to control the viscosity of the water-trapping agent, and it may be thus in direct contact with the organic layer when or after being supplied into the structure. Of course, the organic solvent itself is not necessary for water-trapping or drying performance of the water-trapping agent.
For the reasons set forth above, the organic solvent should be evaporated to dryness after supplying the water-trapping agent. However, the dried water-trapping agent is likely to be hardened, thereby making internal filling or charging difficult or impossible, and causing the organic layer to break due to the contact with the hardened water-trapping agent.
Also, this type of water-trapping agent has a tendency to crack when adsorbing moisture inside the element. As a result, the light to be emitted is subjected to irregular reflection or scattered reflection, thereby decreasing transmission. For the reason as set forth above, this type of water-trapping agent is not considered to be suitable for, particularly, the top emission-type structure.
Furthermore, in the hollow sealing structure, the organic layer disposed on the element substrate is sealed by the sealing cap, and the drying agent-containing water-trapping agent is applied onto the sealing cap. The organic solvent present in the water-trapping agent can be removed by heating. However, it is difficult to recover the organic solvent evaporated during the drying step. At the same time, it takes long time to complete the drying step.
In order to resolve the above drawbacks and problems, the present invention provides a novel water-trapping agent, and an organoelectronic device using the water-trapping agent therein.